This invention relates generally to the protection of wire ropes from corrosive conditions and more particularly to the sealing of wire ropes against corrosive environments by the use of plastic foam compositions.
Various expedients have in the past been used to bar the entrance of water and moisture into the interior of wire ropes and strands. Such expedients have included the use of heavy lubricants, external plastic coatings and the encapsulation of individual wires, strands or even an entire wire rope in solid plastic sheaths. Lubricants are soon lost from an otherwise unprotected strand or rope while external protective coatings are subject to wear and upon rupture at any point will admit moisture to the interior of the rope or strand. Solid encapsulation, on the other hand, seriously interferes with the flexibility of the rope or strand and is also difficult to attain.
U.S. Pat. Nos. 3,681,911 and 3,778,994 to D. V. Humphries and 3,800,522 to C. R. Hughes et al. as well as several other recently issued patents disclose a successful alleviation of many of these previous problems. In these disclosures a working wire rope or a single working strand is impregnated with a liquid plastic foam composition during fabrication and said liquid is then converted to a flexible foam by the application of heat. The foam material is adherent to the individual wires and because of its low overall density does not decrease the flexibility of the rope or strand. The exterior of the rope or strand may be covered with a thin layer of foam or with a layer of denser plastic or may more preferably be wiped clean, particularly in working ropes and strands, i.e. those which are used over sheaves and pulleys and the like or otherwise used in dynamic operations as opposed to static use such as guy lines and other types of permanent anchor lines. The bare wire surfaces resist abrasion and wear in these cases while the interior foam material between the wires, which preferably closely encloses all but the outer surfaces of the wires, prevents the access of water and moisture to the interior surfaces of the wires.
While these previous wire ropes and strands have been very successful, there are some applications in which it may not be desired to fully impregnate a wire rope with plastic. For example, in some installations it may be desired to make use of a permanently lubricated wire core or fiber core in a rope. Methods of completely or partially encapsulating a lubricant permanently in a wire rope core are disclosed to U.S. Pat. Nos. 3,705,489 to C. W. Smollinger, 3,824,777 to P. P. Riggs and 3,874,158 to F. Chiapetta et al. Where it is desired to use a natural or synthetic fiber core in a wire rope, it has often been found to be impractical to encapsulate all of the outer strands with a plastic foam and then heat cure the assembly all at one time because the heat of the foaming operation deleteriously affects the properties of the fiber core. Most experimental plastic foam impregnated wire ropes have, therefore, been made with the individual strands of the rope impregnated with plastic foam prior to stranding, or closing, of the individual strands together into a rope. In these experimental ropes the core of the rope has been a lubricated fiber core, but lubricated wire rope cores have also been used.
It is often desirable even in plastic foam filled ropes to prelubricate the surface of the strand with a heavy lubricant such as a heavy grease or asphalt composition which serves to protect the outer exposed surfaces of the wires from the environment prior to and during use and also serves during use to lubricate the surface of the rope. Frequently a reel of wire rope will be retained in very corrosive environmental conditions for long periods prior to and in between use. For example, a so-called shrimp rope for use on shrimp boats may remain on a reel in marine environments for several weeks or more prior to use and for shorter intermittent periods during use. While a plastic foam impregnated wire rope will be inherently quite corrosion resistant, as compared with an unimpregnated rope, portions of the outer wires will usually still be exposed and subject to corrosion which may tend to migrate even under the edges of the plastic as corrosion products such as rust lift the edges of the plastic. It has been found, therefore, that it is often desirable to apply the usual outer heavy lubrication ordinarily applied to conventional ropes under such conditions to the foam plastic impregnated ropes as well. Naturally it is desirable for such lubrication to remain on the surface of the rope as long as possible, both for lubrication during use and for corrosion protection.